Gliomas, tumors that originate from glial cells (e.g., astrocytes, oligodendrocytes), are the most common group of primary brain tumors with an estimated incidence in the USA of ~18,500 new cases per year. Patients with glioblastoma multiforme (GBM), the most malignant and lethal astrocytic tumor, have a poor prognosis, with a median survival of ~1 year. Malignant glioma cells are highly invasive and their efficient infiltration into adjacent normal brain tissue prevents complete surgical removal or effective destruction by lethal radiation exposure. The Fn14 gene, initially discovered in our laboratory during a screen for growth factor-inducible genes in murine fibroblasts, encodes a cell surface receptor for the multifunctional cytokine tumor necrosis factor-like weak inducer of apoptosis (TWEAK). We have found that Fn14 gene expression is frequently elevated in glioma cells located in both the tumor core and invasive rim regions of GBM specimens. We have also shown that Fn14 overexpression in transfected cells activates the nuclear factor (NF)-kB signaling pathway. We hypothesize that Fn14 overexpression in glioma cells promotes constitutive, ligand-independent activation of the NF-kB signaling pathway, and that the hyperactivation of this pathway contributes to glioma cell invasiveness in vivo. In addition, we hypothesize that the Fn14 cell surface receptor may be a novel target for ligand:cytotoxin fusion protein-based brain tumor therapy. Accordingly, the Specific Aims of this proposal are:(1) To determine whether Fn14 overexpression in transfected human glioma cell lines stimulates NF-kB activation, cell proliferation, cell migration, matrix metalloproteinase production or cell invasion in vitro, (2) To determine whether Fn14 overexpression in transfected human glioma cell lines stimulates cell invasion ex vivo or in vivo, (3) To determine whether NF-kB activation is critical for Fn14-mediated glioma cell invasion, and (4) To determine whether aTWEAK-Pseudomonas exotoxin fusion protein is cytotoxic to Fn14-positive glioma cells. Relevance to public health: Many brain tumors are highly invasive and consequently very difficult to treat. The proposed studies will examine whether a protein named Fn14 contributes to tumor cell invasiveness and whether it could be a novel molecular target for anti-invasive therapy in humans.